.TH std::is_rvalue_reference 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::is_rvalue_reference \- std::is_rvalue_reference

.SH Synopsis
   Defined in header <type_traits>
   template< class T >              \fI(since C++11)\fP
   struct is_rvalue_reference;

   std::is_rvalue_reference is a UnaryTypeTrait.

   Checks whether T is an rvalue reference type. Provides the member constant value
   which is equal to true, if T is an rvalue reference type. Otherwise, value is equal
   to false.

   If the program adds specializations for std::is_rvalue_reference or
   std::is_rvalue_reference_v, the behavior is undefined.

.SH Template parameters

   T - a type to check

   Helper variable template

   template< class T >
   inline constexpr bool is_rvalue_reference_v =                          \fI(since C++17)\fP
   is_rvalue_reference<T>::value;



Inherited from std::integral_constant

.SH Member constants

   value    true if T is an rvalue reference type, false otherwise
   \fB[static]\fP \fI(public static member constant)\fP

.SH Member functions

   operator bool converts the object to bool, returns value
                 \fI(public member function)\fP
   operator()    returns value
   \fI(C++14)\fP       \fI(public member function)\fP

.SH Member types

   Type       Definition
   value_type bool
   type       std::integral_constant<bool, value>

.SH Possible implementation

   template<class T> struct is_rvalue_reference : std::false_type {};
   template<class T> struct is_rvalue_reference<T&&> : std::true_type {};

.SH Example


// Run this code

 #include <type_traits>
 #include <iostream>

 class A {};

 static_assert
 (
     std::is_rvalue_reference_v<A> == false and
     std::is_rvalue_reference_v<A&> == false and
     std::is_rvalue_reference_v<A&&> != false and
     std::is_rvalue_reference_v<char> == false and
     std::is_rvalue_reference_v<char&> == false and
     std::is_rvalue_reference_v<char&&> != false
 );



 template <typename T>
 void test(T&& x)
 {
     static_assert(std::is_same_v<T&&, decltype(x)>);
     std::cout << "T\\t" << std::is_rvalue_reference<T>::value << '\\n';
     std::cout << "T&&\\t" << std::is_rvalue_reference<T&&>::value << '\\n';
     std::cout << "decltype(x)\\t" << std::is_rvalue_reference<decltype(x)>::value << '\\n';
 }

 int main()
 {
     std::cout << std::boolalpha;
     std::cout << "A\\t" << std::is_rvalue_reference<A>::value << '\\n';
     std::cout << "A&\\t" << std::is_rvalue_reference<A&>::value << '\\n';
     std::cout << "A&&\\t" << std::is_rvalue_reference<A&&>::value << '\\n';
     std::cout << "char\\t" << std::is_rvalue_reference<char>::value << '\\n';
     std::cout << "char&\\t" << std::is_rvalue_reference<char&>::value << '\\n';
     std::cout << "char&&\\t" << std::is_rvalue_reference<char&&>::value << '\\n';

     std::cout << "\\ntest(42)\\n";
     test(42);

     std::cout << "\\ntest(x)\\n";
     int x = 42;
     test(x);
 }

.SH Output:

 A       false
 A&      false
 A&&     true
 char    false
 char&   false
 char&&  true

 test\fB(42)\fP
 T       false
 T&&     true
 decltype(x)     true

 test(x)
 T       false
 T&&     false
 decltype(x)     false

.SH See also

   is_lvalue_reference checks if a type is an lvalue reference
   \fI(C++11)\fP             \fI(class template)\fP
   is_reference        checks if a type is either an lvalue reference or rvalue
   \fI(C++11)\fP             reference
                       \fI(class template)\fP
